Radio beam system



I June 11, 1940. WOLFF Y 2,203,807

RADIO BEAM SYSTEM Filed Aug. 18, 1957 2 Sheets-Sheet 2 4 Q TRH/WM/TTE/i 3 5 7 Q Q s f 500 gm S 2 Q l v i a). hag Q g 13 7 a w: 5 14 7 Snventor Irvin W01 Patented June 11, 1940 UNITED STATES PATENT OFFICE RADIO BEAM SYSTEM Delaware Application August 18, 1937, Serial No. 159,641

8 Claims.

This invention relates to a radio beam system. More particularly, it relates to a radio beam protective system which is normally maintained in a state of balance which is independent of the transmitter output and receiver sensitivity.

It has been proposed that an ultra high frequency radio beam from a transmitter be directed toward a radio receiver to protect a region between the two devices. If the ultra high fre- 10 quency beam be intercepted by a body moving between the transmitter and receiver, the beam will be reflected, scattered, or absorbed, at least in part, whereby more or less energy will be received. The change in received energy may be 15 used to operate an alarm. Protective systems of the radio beam type may be used to protect prison walls, warehouses, and may be applied to other uses.

One of the diflicuties with the foregoing system so is that a variation in receiver sensitivity or output, or of transmitter output, due to variations of the power supply or any other cause, may sufficiently change the amount of the received energy to operate the alarm. The operation of the 25 alarm by means other than the interception of the beam is undesirable.

One proposed method of reducing the possibility of spurious alarm signals resulting from variations in the transmitter or receiver has been the use of a pair of balanced receivers. Balanced receivers may make the system substantially independent of transmitter output but the operation depends upon the balance of the receivers which may become unbalanced because of a varia- 35 tion in their relative sensitivity.

One of the objects of this invention is to provide a radio beam protective system which will be independent of the radio transmitter output and radio receiver sensitivity.

40 Another object is to provide means for modulating two portions of an ultra high radio frequency beam with different audio frequencies, or difierent phases of the same frequency, and to receive such modulated beam on a single receiver 4 which includes demodulating, frequency separating or phase balancing means, and a balanced alarm.

An additional object is to provide a radio beam protective system with two different modulating 50 frequencies or phases and to balance these frequencies or phases at a receiver an clgndicate unbalance by an, alarm.

In the accompanying drawings:

Figure 1 is a schematic diagram of one em- 55 bodiment of the invention,

Figure 2 is a diagram of a modified embodiment of thejinvention,

Figure 3 is a schematic diagram of another embodiment of my invention illustrating a single frequency two phase modulation of the protective 5 beam, and

Figure 4 is an elevational view of a transmitter and a plurality of modulators.

In describing the invention, reference will be made to the drawings in which similar reference numerals will be used to indicate similar ele ments. An ultra high frequency transmitter I is connected to a dipole antenna 3 which is suitably located within a reflector 5. A pair of gas modulators 7, 9 are positioned in the path of the beam whereby different portions of the beam may be modulated.

By way of example, one portion of the beam may be modulated by an alternating current of a frequency of sixty cycles per second; the other portion by an alternating current of frequency of five hundredcycles per second. Several suitable types of modulators for ultra high frequency waves are described in U. S. Patent 2,047,929, issued July 14, 1936, to E. G. Linder, and entited Ionic modulator, U. S. Patent 2,073,642, issued March 16, 1937, to A. A. Linsell, and entitled Ultra short wave modulated carrier wave radio communication system and U. S. Patent 2,078,- 302, issued April 27, 1937, to I. Wolff, and entitled Modulating systems for short waves. The modulating currents may be supp'ied from alternators H, l3 and regulated by variable resistors IS, IT or potentiometers l9, 2|. In place of alternators, thermionic oscillators may be used. It is desirable that the modulating currents be substantially constant in both amplitude and frequency.

The beam radiated from the antenna 3, after having portions modulated by the modulators l, 9, is received by a second dipole antenna 23. The second dipole antenna may be suitably positioned within a reflector 25. The reflector 25 is focused on the transmitter to obtain a maximum response. The dipole 23 is connected to a detector and amplifier 21. The output of the amplifier is impressed on a frequency separator 29. The frequency separator may be any conventional form of filter for separating the currents of the two-modulation frequencies; e. g., 60 cycles 5 per second and 500 cycles per second.

The modulation currents, after separation, are impressed on a pair of rectifiers 3 I, 33. The rectifiers are connected either directly to a balanced indicator 35 or to the indicator through filters 31,

39 and potentiometers 4|, 43. The filters are used to smooth out any ripple in the rectified currents. The potentiometers are used to initially balance the currents which are impressed on the indicator 35.

In the operation of the system of Fig. 1, the radiated beam is projected toward the receiver. One portion of the beam is modulated by the low frequency modulator I; the other portion of the beam is modulated by the high frequency modulator 9. The relative percentage modulation of the different portions of the beam can be regulated by adjusting the currents flowing through the modulators. It should be understood that the modulated portions of the beam can be oriented to provide the maximum protection to the region through which the beam is radiated. By way of example, the four quadrants of a beam may be modulated in pairs by means of the modulators shown in Fig. 4.

The modulated beam is detected and the two modulation currents amplified. The amplified currents, being of substantially different frequencies, may be readily separated and rectified. If the rectified currents are adjusted until they are equal and opposite and impressed on the indicator 35, no indigationlar m will be made because of the bal nced condition of the rectified currents. If the rectified currents pulsate and cause movements of the indicator 35, filters may be used to smooth out such pulsations.

In the foregoing system, variations of the transmitter output or receiver sensitivity will have practically no effect on the device because the alarm is operated by the differentiation of the modulation currents only. If an object enters the beam after the balance has been effected, ordinarily one of the portions of the beam will be varied and therefore different modulation currents will be derived at the receiver. The difference in modulation currents will operate the alarm. The beam may be modulated in a plurality of portions, such as the quadrants of Fig. 4. The several modulated portions may be arranged so that it is practically impossible for an object to pass through the beam without actuating the alarm.

The system of Fig. 2 is essentially similar to that of Fig. 1. In the former circuit, a reflector 45, and a pair of reflectors 41, 49 are included at the transmitter. The relative size of the reflectors 45, 41, 49 is not to be judged from the illustration; in practice, the last mentioned refiectors would have an effective area of the order of the parabolic reflector 5. The modulators 5|, 53 each include a grid electrode on which the modulating currents are impressed. The modulating currents are adjusted by potentiometers l9, 2| which are connected across the alternators ll, l3. The receiver of Fig. 2 is similar to the receiver of Fig. 1. A lamp 55 or other suitable means, located at the receiver, may be connected to the transmitter to indicate any power interruptions. The indicatouiqnay-dnclude both visible and audible means for indicating the alarm signal.

K'sErTgTe frequency two phase modulation system is schematically illustrated in Fig. 3 in which the transmitter l impresses ultra high frequency currents on the antenna 3. Waves from the antenna 3 are reflected from the reflectors 45, 41 and 49 to thereby divide the radiated waves into portions which pass through the modulators I, 9 before reaching the receiving antennas 3|, demodulator-amplifier 21 and alarm 35. The modulators, instead of being near the transmitting antenna, are located near the receiving antennas 3|. Although I prefer space modulators," that is, modulators which act directly on the radiated wave, other well known types of modulators may be included in the receiver circuit.

In the instant system, single frequency opposed phase modulation is used. An alternating current from a generator l3 or the like is impressed on a transformer 51 which includes a center tapped secondary 59. If the transformer is symmetrically arranged with respect to the center tap, the secondary currents in the opposite halves will be in substantially 180 phasal relation. These currents are impressed on potentiometers GI, 63 and variable capacitors 65, 61. The potentiometers and capacitors are adjusted to impress currents of opposite phase on the modulators l, 9 which are connected to the potentiometers, so that equal and opposite effects are produced at the receiver.

As thus arranged, the upper and lower portions of the beam of ultra high frequency energy from the transmitter will be equally and oppositely modulated. The receiver which demodulates the beam will impress demodulated currents of equal and opposite phases. These currents are balanced in the alarm qr ingl icator 35. If either the upper ofldwf fib'itions of the beams are intercepted, the demodulated or output currents will no longer be balanced and therefore the alarm will be actuated.

This invention has been described as a radio beam protective system in which different portions of a radio beam are modulated by two currents of different frequencies or phases. The receiver of the system is responsive to the beam frequency. The received currents include the different phases or modulation frequencies which are separated, and balanced against each other. The balanced currents are impressed on an alarm. When a portion of the beam is intercepted, the received modulation currents being no longer balanced operate the alarm.

I claim as my invention:

1. The method of indicating the presence of a foreign object in an area to be protected by means of a radio beam system which includes, radiating a radio beam through said area, modulating different portions of said beam by currents of different characteristics, receiving said beam, demodulating said beam to derive currents corresponding to said currents of different characteristics, rectifying said derived currents. applying said currents equally and oppositely to thereby obtain a balance, and indicating changes in said balance due to the presence of said foreign object in said beam.

2. The method of indicating the presence of a foreign object in an area to be protected by means of a radio beam system which includes radiating a radio beam through said area, modulating different portions of said beam by currents of different characteristics, receiving said beam, demodulating said beam to derive currents corresponding to said currents of different characteristics, separating said derived currents into currents of said different characteristics, rectifying said separated currents, applying said currents equally and oppositely to thereby obtain a balance, and indicating changes in said balance due to the presence of said foreign objects in said beam.

3. The method of indicating the presence of a foreign object in an area to be protected by means of a radio beam system which includes radiating a radio beam through said area, modulating difierent portions of said beam by currents of different characteristics, receiving said beam, demodulating said beam to derive currents corresponding to said currents of different characteristics, separating said derived currents into currents of said different characteristics, rectifying said separated currents, filtering said rectified currents, applying said currents equally and oppositely to thereby obtain a balance, and indicating changes in said balance due to the presence of said object in said beam.

4. The method of indicating the presence of a foreign object in a region to be protected by means of a radio beam system which includes the steps of radiating a radio beam through said region, modulating different portions of said beam by modulations of diiferent characteristics, receiving said beam, demodulating said beam to derive currents corresponding to said modulations, combining said derived currents to obtain a balance, and indicating any change in said combination.

5. In a radio protective system, means for radiating unmodulated radio frequency waves, separate means for receiving different portions of said waves, means adjacent each of said receiving means for differentially modulating said waves, means for demodulating each of said received waves to obtain modulation frequency currents, means for combining said currents to obtain a balance, and means for indicating a change in said balance.

6. In a radio protective system, a source of radio fequency waves, separate means for receiving different portions of said waves, means for modulating said waves by currents in phase opposition at respective receiving means, means for demodulating said received waves, means for combining said demodulated currents to obtain a balance, and means for indicating a change in said balance.

7. In a radio protective system, means for radiating unmodulated radio frequency waves, separate means for receiving difierent portions of said waves, means adjacent said receiving means for modulating said Waves before reception by each of said separate receiving means, means for obtaining modulation frequency currents from said received waves, means for combining said currents to obtain a balance, and means for indicating a change in said balance due to the interruption of a portion of said unmodulated radio frequency waves.

8. In a radio frequency protective system, a source of high frequency radio waves, means for spreading said waves through separate paths through the region to be protected, separate means for receiving difierent portions of said waves, means adjacent said separate receiving means for modulating said waves by currents in phase opposition, means for demodulating said received waves, means for combining said demodulated currents to obtain a balance, and means for indicating a change in said balance due to the interruption of the waves in one of said paths.

IRVING WOLFF. 

